2 Commits

Include renames

Author	SHA1	Message	Date
jaap-jan	c2c860b4f2	Give the seated user the TPM, so nobody has to join the tss group ... ADR 0007 decision 4 refused this a commit ago, on the grounds that widening access to the machine's TPM is a system-wide decision an application package should not make for an administrator. That refusal is overturned here, and the reasoning it is replaced with is narrower rather than louder — because the refusal had treated "widen access" as one thing when it is two. Adding a person to `tss` is what the refusal was really about, and it stays the wrong answer: permanent, effective over SSH, applying whether or not they are at the keyboard, and needing an administrator and a fresh login before the feature appears at all. Tagging /dev/tpmrm0 with `uaccess` is a different thing. It is systemd's own mechanism for this exact question — the one /dev/dri, webcams, scanners and FIDO keys already use — and logind grants the ACL to the user of the *active local session*, then takes it back when that session ends. Not over SSH, not on an inactive VT, not to daemons. The rule changes neither the mode nor the group, so everything that worked before still works and the ACL is layered on top. tpmrm and never tpm, which is what makes it defensible at all: /dev/tpm0 is the raw device and is exclusive, where /dev/tpmrm0 is the kernel's resource manager, which virtualises handles and isolates callers precisely so that more than one unprivileged program can use the chip. ◆ THE COST IS A DENIAL OF SERVICE AND NOT A DISCLOSURE, AND IT IS WRITTEN DOWN. TPM objects are protected by their own auth values, so this lets nobody read anybody else's sealed data. What it allows is *failed* attempts — and a TPM answers enough of those by locking out everyone, which is the same anti-hammering this project relies on to make a four-digit PIN safe. On a machine that unlocks its disk with the TPM at boot, somebody sitting at it can trip that and stop the next boot from unlocking until it recovers. An administrator who does not accept that masks the file: sudo ln -s /dev/null /etc/udev/rules.d/71-dodossh-tpm.rules which is the standard override, survives upgrades, and puts DodoSSH back to behaving as though the machine had no TPM. That is in the rule's own comments, because the person who needs it is reading the file rather than the ADR. Numbered 71 because 60-tpm-udev.rules is what creates the node's ownership and 73-seat-late.rules is what turns the tag into an ACL; verified in that order on Fedora 44, along with `udevadm verify` accepting the file and the mask being reported as "masked by previous entry". %post reloads and replays it against the tpmrm subsystem, because a rule that waits for a reboot is a feature that does not work on the day it is installed. Both channels install the same path deliberately: this is about the machine's TPM rather than about either build, the file is byte-identical from both, and giving each its own copy would mean removing one package silently revoked the other's access. Phase 19 grew a check that the ACL exists for the local session and does *not* exist for an SSH one, and another that masking the rule really does put the machine back — then tells you to undo it before the checks that follow. Also recorded, after it cost five confusing failures: swtpm serves exactly one client, so a shell readiness probe sitting on the port makes the whole device-key suite fail with "The TPM closed the connection" and nothing pointing at why.	2026-08-22 20:38:22 +02:00
jaap-jan	4552538533	Let the Linux head check for updates, and seal its device key in the TPM ... Two things the RPM shipped without, and the reason they arrive together is that both are the same question — what may this platform ask of the machine, and what must it not ask of the user. ◆ UPDATES: THIS CLIENT CHECKS AND FETCHES, AND PACKAGEKIT INSTALLS. ADR 0013 rule 11 said there was no updater at all, and that went too far. It conflated noticing that a newer build exists with installing it: the second is what the trust argument is about, and the first is not — a client that checks a fixed address and tells you what it found has taken no capability from anybody. Written as a flat refusal, the rule bought its safety by paying a cost that was avoidable, and the ADR now says so in its own words. So LinuxUpdateChannel reads the rolling nightly release, compares versions the way rpm compares them, downloads the package, verifies its digest and hands the file to PackageKit over gdbus. Polkit asks; the user may say no; nothing is torn down before the answer, because ApplyingEndsTheProcess is false and the shell already knows what that means — it is the phone's shape, and declining an update must not cost somebody their open shells. Three details that are load-bearing rather than incidental: - The comparison is rpmvercmp and not SemVer, because rpm is what will accept or refuse the install. Same argument ADR 0014 makes for versionCode. The installed side is read out of the rpm database rather than derived from the assembly, so the SemVer-to-rpm translation exists in exactly one place. All 28 expected values in RpmVersionTests came out of rpm itself rather than out of a reading of the algorithm. - The digest is checked and is not a signature. Velopack verifies its own downloads and Android checks a signature; an RPM over HTTPS has neither. The manifest names a SHA-256 and a mismatch deletes the file rather than leaving something installable-by-hand in the profile directory. - ONLY_TRUSTED is cleared, which is what routes the request to polkit's package-install-untrusted action. The package is unsigned, so requiring trust would fail every update at the last step. ◆ THE DEVICE KEY: SEALED IN THE TPM, BEHIND A PIN THE TPM CHECKS. ADR 0007's amendment is the bar: a gate inside the process is not a gate. The key is sealed into a TPM 2.0 keyedhash object whose userAuth comes from a PIN, so unsealing is a command the chip refuses; the blob is encrypted to the storage hierarchy and is useless on any other machine; nothing here ever compares a PIN. The sealed object deliberately carries no NoDA attribute, and that one omission is the whole reason four digits is enough: every wrong answer advances the TPM's dictionary-attack counter and the chip stops answering entirely once it trips. Measured at four wrong tries against a software TPM, after which the correct PIN gets nothing either. It is asserted by a test rather than left to a reading of the template, because removing the attribute leaves every other assertion passing. This is weaker than Hello and Touch ID and the difference is invisible, so it is written down in three places rather than smoothed over: those raise their prompt from inside the platform and this one is a window we draw. The prompt is deliberately plain for that reason — teaching people that a convincing DodoSSH PIN box is a system dialog is the one thing this design must not do. Rejected, each for failing the amendment: the Secret Service API, which has no per-use consent and is DPAPI's shape exactly; fprintd, which answers a question and holds nothing, so skipping the call skips the gate; and a polkit-gated root helper, which would work and puts a privileged component in a package that installs nothing setuid. Availability is narrower than "has a TPM": on Fedora /dev/tpmrm0 is root:tss and desktop users are not in tss, so the ordinary case reports unavailable and keeps asking for the passphrase. Shipping a udev rule to widen that is refused — it is the administrator's decision, not an application package's. ◆ WHAT IS ACTUALLY VERIFIED, SINCE THAT IS THE PART THAT USUALLY ISN'T. This is the only device key store in the repository with real coverage, and it is only possible because the PIN is a delegate and the TPM is a device: seal, unseal, wrong PIN, lockout, decline and a foreign blob all run unattended against a software TPM. Windows and macOS cannot be tested at all — their prompts block a suite forever, which WindowsDeviceKeyStoreTests records. TSS.Net's own TcpTpmDevice cannot reach swtpm: it opens the platform socket too and exchanges a handshake only the Microsoft reference simulator answers, so Connect() blocks with no error and no timeout. SoftwareTpm speaks the data channel and nothing else. The suite also lied once and was fixed: the lockout test trips shared state, and without a DictionaryAttackLockReset in Dispose every later test got null from a correct PIN — six of them assert null and passed for entirely the wrong reason. End to end on a real Fedora 44: a genuine linux-x64 publish packages, installs, and every DT_NEEDED in the installed tree resolves except liblttng-ust, which is the one this spec deliberately excludes. What no runner covers is /dev/tpmrm0, PackageKit and polkit, and Phase 19 grew five checks for exactly those. Also fixed: the magic-bytes literal picked up raw control characters, which made LinuxDeviceKeyStore.cs binary to git — no diffs and no line-ending normalisation.	2026-08-22 20:02:30 +02:00